This application claims the priority of German patent document 199 55 646, filed 19 Nov. 1999 (PCT International Application No. PCT/EP00/11186, filed 11 Nov. 1999), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for assigning a tool to a workpiece on an assembly line.
In the assembly line production of workpieces, tools operated by workers can only rarely be assigned to a certain part to be worked. In particular, it is impossible to determine where a tool is situated with respect to a workpiece located on an assembly line. Thus, it could happen, for example, that workpieces, such as vehicles, leave the assembly without the certain screwed connections. Checking is not easily performed.
It is an object of the present invention to provide a method and apparatus which permit the assignment of tools to a workpiece conveyed on an assembly line.
This and other objects and advantages are achieved by the method and apparatus according to the invention, in which the position of a tool is detected either relative to a workpiece or relative to a stationary system of coordinates and is assigned to a workpiece situated on the assembly line. In this case, an identifier (for example, a production or chassis number) is assigned to each workpiece, and the position of the tool is detected by analysis of the transit times of signals emitted by a transmitter and received by a receiver. The position of the tool can be computed by way of trigonometric functions. According to an embodiment, a transmitter or a receiver is arranged on the tool. The arrangement of a receiver on a tool has the advantage that disturbances caused by the tool operation have a less interfering influence. Depending on whether a transmitter or a receiver is arranged on the tool, the pertaining counterparts (the receivers or the transmitters) are provided in the area of the assembly line.
According to a preferred embodiment, the receivers or transmitters not arranged on the tool are stationary in space. As a result of the analysis of the transit times between the transmitters and the assigned receivers, the absolute position of the tool can be indicated in the space.
In the case of a tool which is movable in all direction, three transmitters (or alternatively, three receivers) are required in order to achieve an unambiguous localization in space. However, when the tool is movable in only one defined direction with respect to the vehicle, a single transmitter (or alternatively construction, a single receiver) may be sufficient.
According to another embodiment, a transmitter (alternatively a receiver) can also be moved along on the assembly line, for example, together With a certain workpiece, so that, by distance measurement, information can already be derived with respect to the distance of the tool from the transmitter (alternatively, the receiver) arranged on the workpiece.
By means of the already existing knowledge of identifiable workpieces on the assembly line and their known momentary positions, a time-related assignment of a tool to a workpiece can be made from the position of the receiver (alternatively, the transmitter) arranged on the tool. According to the detection rate of the tool position, precise information can therefore be obtained as to whether the tool has been guided to a particular position of a workpiece that has a known identification. By storing these data, an overall check is possible as to whether a tool has been guided to a workpiece.
The method and apparatus according to the invention can basically be used for all tools for which the assignment to a workpiece is important. On the whole, the present invention is less expensive and can be used in a more flexible manner than known mechanical devices.
According to an advantageous embodiment, ultrasonic devices can be used as the transmitters and receivers. The transmitters can emit gradually triggered signals; or as an alternative, each transmitter emits characteristic signals. The emitted signals are received by the receiving unit and are assigned to the corresponding transmitters. From the transit times of the signals, the distances can then be computed between the respective transmitters and receivers and the position of the tool can be determined in this manner.
As mentioned above, when at least three transmitters (alternatively, three receivers) are used, an unambiguous position determination can be made also in the case of a tool which is freely movable. In this case, a zero point can be determined and the position of the tool can be indicated with respect to this zero point.
For checking the assembling progress, it is advantageous for the data for the assignment of a tool to a vehicle supplied by an assignment unit to be stored in a memory, particularly a non-volatile memory. The data can also be received in a memory medium to be stored, so that the assembling progress can be precisely checked for an extended time period.
According to a preferred embodiment, it is also detected and recorded whether the tool (for example, an electric screwdriver), has been operated according to its function. Thus, not only can the guiding of the tool to a certain vehicle be reconstructed, but also its proper functional operation at a certain point. For example, in the case of an electric screwdriver, it can be determined by way of the applied torque whether the screwed connection was carried out correctly. When the electric screwdriver is operated without applying the latter to the screw or when a screw is twisted off, no expected torque will occur so that no proper screwed connection on a defined identifiable workpiece can be reported. Such feedback of properly implemented working steps can take place in the case of all operable tools and can, in turn, be assigned to workpieces.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.